Cardiac arrhythmias are a leading cause of stroke, heart disease, and sudden death. The physiological mechanism of arrhythmia involves an abnormality in the electrical conduction of the heart. There are a number of treatment options for patients with arrhythmia that include medication, implantable devices, and catheter ablation of cardiac tissue.
Traditionally, the arrhythmia is studied and diagnosed by “electrically mapping” the heart with catheters inserted through the vasculature into a heart chamber. Traditionally, the electrical activity of the heart is acquired directly by “in-contact” mapping of the interior wall surface of a heart chamber. In this technique electrodes are placed in intimate contact with the heart wall and the voltage at that location is recorded and plotted against time for display to the physician. The in-contact catheters may be large and essentially fill the entire heart chamber, or they may be smaller and moved around in the heart chamber to sequentially map various areas of the heart. Mechanically, the in-contact mapping catheters are “soft” so that they can conform to the heart chamber. Softness is required so the electrodes come into intimate contact with the heart wall while accommodating wall motion of the beating heart.
For example, multiple electrode in-contact mapping catheters are known from U.S. Pat. No. 5,628,313 to Webster that shows a so-called “basket,” catheter. In use, this very flexible and conformal catheter is deployed in the heart and presses individual electrodes against the chamber wall for full chamber contact mapping of a beating heart. Smaller multiple electrode catheters are known as well. For example, the U.S. Pat. No. 5,279,299 to Imran illustrates techniques for creating smaller catheter arrays that are used to selectively contact map portions of the cardiac chamber. This catheter is flexible and electrodes remain in contact with the wall even when the catheter shaft is displaced slightly. In each of these examples, the limbs of the catheter are very flexible and gently contact the chamber wall while the wall of the heart is moving.
“Non-contact mapping,” also known in the art, is an alternative to in-contact mapping where a catheter array positioned within a chamber is used to collect global electrical information. This global information is then used to compute a solution to the so-called “inverse problem”. The inverse problem of electrophysiology is the calculation of wall electrical potentials from the measured field voltages associated with the wall potentials as measured within the blood pool remote from the chamber wall. The mathematical “solution” displayed to the physician is the computed wall surface voltages that can be used to detect problems in electrical conduction in the heart wall.
Although in-contact and non-contact catheters are used for the same patient indications, they have very different mechanical and electrical requirements. Chief among the requirements of a non-contact catheter is stability of the electrode array. The geometry and locations of the electrodes are assumed for the inverse solution calculation and need to be known with great precision. Small error in electrode position can render large discrepancies in computed mathematical solution. In addition, controlled movement of the electrode array within the chamber of interest is necessary in order to improve the accuracy of the non-contact map. Deployment of the electrode array into a repeatable precisely known shape, while supporting controlled movement of the catheter, pose particularly complex and novel requirement on the catheter design.
Once the anatomic origin of problems in electrical conduction are identified, the physician may proceed to ablate the offending tissue, thus treating the arrhythmia. Catheter ablation procedures have evolved in recent years to become an established treatment for patients with a variety of supraventricular and ventricular arrhythmias. The typical catheter ablation procedure involves mapping of the heart tissue in order to identify the site of origin of the arrhythmia, followed by a targeted ablation of the site with an RF catheter. The procedure takes place in an electrophysiology laboratory and takes several hours most of which is spent mapping the electrical conduction in the heart.
Although in-contact and non-contact mapping methods are known in the art and various deflectable, displaceable and deployable catheters are known as well, there is a continuing need to improve the accuracy, stability and maneuverability of such devices so that they can be more widely used, especially as an adjunct to cardiac ablation procedures.